This invention concerns refractory compositions and particularly such compositions adapted to placement by gunning.
In gunning, refractory materials are placed, for example on a furnace wall, by projecting them through a gun or nozzle, the propelling force being, for example, compressed air. Water is added to the composition either before the gunning operation (as in slurry gunning, where sufficient water is added to the dry refractory composition to form a slurry, which is then projected through a nozzle into place) or during the gunning operation (as in nozzle gunning, where water is added to the dry refractory through a water ring placed just before the gun nozzle). This invention is concerned with refractory compositions which are particularly adapted for nozzle gunning.
Among the characteristics desired in a gun mix are that it move smoothly through the gun, be projected onto the furnace wall or other target without undue dusting, have low rebound, adhere well to the wall, set relatively fast (so that a reasonable thickness of refractory can be placed without falling off), and have a relatively wide range of water contents within which it exhibits the above desired characteristics. In addition, it should have the usual characteristics desired of a refractory, for example good density, good strength, and ability to withstand the high temperature environment in which it will be used.
Over the years, many different bonding systems have been suggested for gun mixes in an attempt to obtain the best balance of the desired characteristics mentioned above. For example, U.S. Pat. No. 4,001,029 discloses a refractory composition suitable for nozzle gunning which is bonded with aluminum sulfate and hydrated lime (the bond disclosed and claimed in that patent being sometimes hereafter referred to in the specification and claims as the "aluminum sulfate and lime" bond); U.S. Pat. No. 4,244,744 discloses a refractory gun mix containing (as bond) sodium silicate and gypsum (the bond disclosed and claimed in that patent being sometimes hereafter referred to in the specification and claims as the "sodium silicate and gypsum" bond); and U.S. Pat. No. 4,276,091 discloses a composition suitable for gunning with a bonding system of alkali metal phosphate and hydrated aluminum sulfate (the bond disclosed and claimed in that patent being sometimes hereafter referred to in the specification and claims as the "aluminum sulfate and phosphate" bond). As is common with gun mixes, the compositions described in the foregoing patents will often contain bentonite.
Refractory compositions have also been suggested which attempt to combine in one composition the characteristics desired in a ramming mix, a castable, and a gun mix. For example, U.S. Pat. No. 3,879,208 discloses a refractory composition suitable for forming a monolithic structure by ramming, gunning, or casting containing (as bond) aluminum sulfate and an organic acid or salt thereof, with or without the addition of a boron compound (the bond disclosed and claimed in that patent being sometimes hereafter referred to in the specification and claims as the "aluminum sulfate and organic acid" bond); and U.S. Pat. No. 4,149,897 discloses a refractory composition suitable for ramming, casting, or gunning bonded with magnesium sulfate, sodium gluconate, and a soluble boron compound (the bond disclosed and claimed in that patent being sometimes hereafter referred to in the specification and claims as the "magnesium sulfate, sodium gluconate, and soluble boron" bond).
The disclosures of the patents mentioned above are incorporated herein by reference.
Unfortunately, it is often necessary to compromise between the properties desired in a gun mix and those desired in a castable (high density, for example) or a ramming mix (explosion resistance, for example). In other words, it may not be possible to obtain the highest density and strength in a composition which has good gunning characteristics. Similarly, it is often necessary to compromise between gunning characteristics and the desired refractory properties such as high temperature strength, erosion resistance, and the like. Accordingly, the refractories manufacturer is constantly seeking the best combination of properties he can achieve in a refractory composition.
The present invention provides such an improved refractory composition suitable for nozzle gunning. More specifically, it provides a composition which combines good gunning properties such as good build-up and low rebound with good refractory properties such as high strength.